利用脉冲堆积效应实现鲁棒低信噪比隐蔽通信链路
Utilizing Pulse Pileup Effect in Development of Robust Low-SNR Covert Communication Links
摘要：
与其他扩频技术相比，具有相对低的脉冲到达率的宽带脉冲串可能被认为不适合于隐蔽通信。这种脉冲串的高波峰因数对于发射机硬件来说可能是极其繁重的，并且它使得即使在非常低的信噪比下也可以容易地检测到脉冲串。此外，可能出现的是，由多个用户共享宽带信道将需要明确分配每个子信道的脉冲到达时间，这在大多数情况下是不切实际的。另一方面，通过宽带脉冲序列的消息传递具有许多吸引人的特征。其中包括易于同步和异步脉冲检测，以及动态信道可重新配置性（例如，改变扩频因子）。有利地，脉冲训练的波峰因数以及其表观时间和幅度结构可以容易地且可逆地通过简单的线性滤波来控制。例如，可以使发送的脉冲训练在统计上与在相同谱带中观察到的信道噪声（例如，热噪声）的高斯分量不可区分，而接收的信号将是设计的高波峰因数宽带脉冲训练。在本文中，我们利用所谓的脉冲堆积效应来执行这种可逆控制的脉冲训练结构，使更广泛地使用这种方法的合成鲁棒的低信噪比隐蔽通信链路。我们特别关注接收机中的同步脉冲检测，它提供了更好的信道频谱利用率。
英文摘要：
In contrast to other spread-spectrum techniques, wideband pulse trains with relatively low pulse arrival rates may be considered unsuitable for covert communications. The high crest factor of such trains can be extremely burdensome for the transmitter hardware, and it makes the pulse trains easily detectable even at very low signal-to-noise ratios. In addition, it may appear that sharing the wideband channel by multiple users would require explicit allocation of the pulse arrival times for each sub-channel, which would be impractical in most cases. On the other hand, messaging by wideband pulse trains has many appealing features. Among those are the ease of synchronous as well as asynchronous pulse detection, and on-the-fly channel reconfigurability (e.g. changing the spreading factor). Favorably, the crest factor of a pulse train, as well as its apparent temporal and amplitude structure, can be easily, and reversibly, controlled by simple linear filtering. For example, a transmitted pulse train can be made statistically indistinguishable from the Gaussian component of the channel noise (e.g. the thermal noise) observed in the same spectral band, while the received signal will be the designed high-crest-factor wideband pulse train. In this paper, we utilize the so-called pulse pileup effect to perform such reversible control of the pulse train structure, enabling a wider use of this approach for synthesis of robust low-SNR covert communication links. We place a particular focus on the synchronous pulse detection in the receiver, that provides a better utilization of the channel spectrum.
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